Silver is traditionally deposited from alkaline solutions, and particularly cyanide solutions because they are inexpensive and the alkaline cyanide complex is stable toward light. In the late 1950's, acid gold electrolytes were developed when it was discovered that alkali gold cyanide was stable at a pH as low as 3.0. Sodium and potassium silver cyanides do not have the stability of alkali gold cyanide in acid solutions and, consequently, no corresponding acid silver plating solutions were developed until the mid-1960's. It was then discovered that potassium silver cyanide, if buffered in the region of 6.0 or 6.5 to 7, would remain reasonably stable and also that relatively small amounts of an alkali metal or ammonium thiocyanate could stabilize the silver plating bath.
As is apparent, it is desirable to utilize silver plating solutions in which cyanide is not present because cyanide is a well known poison. In addition, some people are allergic to the chemical and develop severe rashes on contact with cyanide. Several attempts have been made in the past to develop an acidic solution without the use of cyanide but these have proven to be sensitive to light and the silver is eventually reduced to the metal by the action of the shorter wave lengths of visible light and also by
It is the object of this invention to provide an acidic silver plating bath which does not employ cyanide and which is stable. This and other objects of the invention will become apparent to those skilled in the art of the following detailed description.